Fail safe magnetic amplifier voltage control system



FAIL SAFE MAGNETIC AMPLIFIER VOLTAGE CONTROL SYSTEM J. DEMEUR June 18, 1968 Flled Dec 17 1965 lllili" y R, I. n MM .4 M a M a United States Patent 3,389,330 FAIL SAFE MAGNETIC AMPLIFIER VOLTAGE CONTROL SYSTEM Jean Demeur, Leeuw-st-Pierre, Belgium, assignor to Ateliers de Constructions Electriques de Charleroi (ACEC), Charleroi, Belgium Filed Dec. 17, 1965, Ser. No. 514,558 Claims priority, applicagiui lgelgium, Jan. 12, 1965,

1 Claim. (51. 323-89) ABSTRACT OF THE DISCLOSURE The present invention relates to saturable reactances for safety circuits and to circuits provided with such reactances.

Certain circuits must be able to provide an intrinsic safety, that is, any fault that accidentally happens to one of the elements of the circuit must never lead to a situation involving a danger. Such circuits are absolutely necessary, namely in railroad signalling, for instance, for controlling the lighting of traffic lights, for automatic railroad crossings, etc. where any circuit fault must result in traffic being forbidden (signals turning to red, gates closing etc.

13s is known, there are certain relay circuits that can provide these conditions but these relays, apart from their high cost and large volume, are subject to wear in their movable members, faults that are not found in equivalent static elements. Unfortunately, the latter generally do not provide the requirements of safety. Particularly, saturable reactances may act as a closed switch if a short circuit takes place between the turns of the windings, which makes them unsuitable for controlling a green light,

for instance.

It is an object of the present invention to provide saturable reactances answering the requirements of safety.

The reactances according to the invention, which comprise two magnetic circuits each carrying a power winding adapted to carry the alternating current to be controlled and provided with a D-C common saturdation winding, are characterized in that each of the two magnetic circuits have a supplementary winding coupled to the power windiii, these two windings being connected in series.

The circuits using the reactances according to the invention are characterized in that they comprise twoof these reactances in series, the voltages of which resulting from their supplementary windings being applied to two inputs of a logic safety element of the type AND the output of which supplies the required safety signal.

The following description refers to two preferred emice The saturable reactance of FIG. 1 comprises two identical magnetic circuits 1 and 2 carrying windings 3 and 4 in series connection with a load, illustrated by a resistance 5, powered by means of'a source of alternating valtage applied across the terminals 6. A D-C winding 7 winds around the two magnetic circuits, the windings 3 and 4 of which are so arranged that their resulting flux in winding 7 is nil. When winding 7 is not energized, it is known that the impedance of windings 3 and 4 is very large so that a veryweak current'fiows through the load 5' which may be considered as not being energized. If a D-C source 8 is applied to the winding 7 by closing, for instance, a switch 9, the two magnetic circuits become saturated and the impedance of the windings 3 and 4 falls practically to zero so that the load 5 is normally energized. The magnetic circuits 1 and 2 carry series connected supplementary windings 10 and 11 respectively, the resulting voltage of which appears across terminals .12. This voltage is used,

' concurrently, with that supplied by another identical bodiments of the invention illustrated in the accompanying drawing wherein:

FIG. 1 is a schematic layout of a saturable reactan'ce; FIG. 2 is a schematic control diagram of an automatic gate for railroad crossing.

saturable reactance in the manner hereinafter explained, by way of example and with reference to FIG. 2.

The rising of the gate is obtained by means of a series D-C motor 13 and it is obtained in raised position by a non-illustrated brake; closing of the gate is obtained by gravity by releasing the brake; the fall is dampened by rheostatic braking of the motor driven by the gate.

Motor 13 is supplied with alternating current from a line 14 through a rectifier 15 connected thereto through two identical inductances 16 and 17 similar to that of FIG. 1. The symbolically shown windings are designated by the same reference numerals as those of FIG. 1 for reactance 16; those of inductance 17 do not carry any numerals since the two reactances are similar.

The supplementary windings 10 and 11 of the two reactances are connected through rectifiers 18 to two control windings of a magnetic logic element 19 such as described in Belgian Patent No. 638,197 filed on Oct. 3, 1963. The primary of this element 19 is supplied with a voltage of apropr-iate frequency from a line 20 and it induces a voltage in the secondary 21 when the resulting flux of the two control windings is nil.

If a short circuit is produced between the turns of one of the two reactances, the resulting voltage of its supplementary windings becomes smaller than the corresponding voltage of the other reactance so that the control windings of element 19 produce, in the magnetic circuit of element 19, a flux that saturates it whereby the voltage in secondary 21 disappears resulting in the locking of the control for the opening of the railroad crossing and the transmitting of a fault signal to the signal room. Consequently, the saturation direct current of the reactances does not flow in conductors 22 and the good reactance remains locked; thus the gate remains closed until repair is made.

Since it is reasonable to ignor the possibility that the two reactances 16 and 17 break down simultaneously, it may be said that the system answers the safety requirements.

Of course, it would be possible to similarly "control other members such as signalling lights; it is also possible to conceive variations to the saturable reactances described above and to their load circuits without departing from the spirit of the present invention.

I claim:

1. A safety circuit comprising:

(a) an alternating current load;

(b) two saturable reactances, each formed of:

two magnetic circuits;

a power winding on each of said circuits;

a common direct current saturation winding wound around both of said magnetic circuits;

a supplementary winding carried by each of said magnetic circuits and magnetically coupled to the corresponding power winding; Y Y

(c) the power windings of said four magnetic circuits and said load being connected in series and to a source of alternating current;

(d) the two common windings of said magnetic circuits being connected in series and to a source of direct current;

(e) a safety logic element of the AND type having two inputs and an output;

(f) the two supplementary windings of each rcactance being in series and across one input of said logic element whereby the resulting voltages thereof are applied across the said two inputs with said output providing a safety signal.

References Cited UNITED MILTON o. I-IIRSHFIELD, Primary Examiner.

W. E. RAY, Examiner. 

